1. Field of the Invention
The present invention relates to a charge pump circuit configured to generate a negative voltage, and particularly to overcurrent protection in such a circuit.
2. Description of the Related Art
In order to convert a DC voltage having a certain level into a DC voltage having a different level, a charge pump circuit is employed. The charge pump circuit has a configuration including several capacitors and several switches. With such a charge pump circuit, a particular capacitor (which is also referred to as a “flying capacitor”) is charged using the input voltage, and energy (charge) stored in the flying capacitor is transferred to another capacitor (which is also referred to as an “output capacitor”) so as to boost or step down the input voltage, or so as to invert the polarity of the input voltage, thereby outputting the output voltage thus boosted, stepped down, or inverted.
FIG. 1 is a circuit diagram which shows a configuration of a charge pump circuit configured to generate a negative voltage. A charge pump circuit 1002 includes a flying capacitor CF, an output capacitor CH, and a first switch SW1 through a fourth switch SW4. The charge pump circuit 1002 alternately repeats the first state φ1 and the second state φ2 so as to generate a negative output voltage Vout, which is then output from the output terminal P2.
In the first state φ1, the first switch SW1 and the third switch SW3 are turned on, and the other switches are turned off. In this state, the flying capacitor CF is charged using the input voltage Vin. Subsequently, in the second state φ2, the second switch SW2 and the fourth switch SW4 are turned on, and the other switches are turned off. In this state, the output capacitor CH is charged using a negative voltage (−Vin). By alternately repeating the first state φ1 and the second state φ2, such an arrangement generates the negative voltage Vout at the output capacitor CH.